Before you go through this article, make sure that you have gone through the previous article on Photoelectric Effect.
We have discussed-
- Photoelectric Effect is a phenomenon of emission of electrons from metal surfaces.
- Photoelectric Effect occurs when a light of suitable frequency falls on the metal surface.
In this article, we will discuss about Photoelectric Cell.
|Photoelectric Cell is a device that converts light energy into electrical energy.|
Also, it may also be defined as-
- Photoelectric cell is an electron tube or a photo tube.
- Electrons initiating an electric current in this electron tube originate by photoelectric emission.
Let us discuss the construction and working of a photoelectric cell.
- Photoelectric cell consists of an evacuated glass containing anode and cathode.
- The cathode is semi cylindrical.
- The cathode is coated with a photo sensitive alkali metal like rubidium, molybdenum etc.
- This is to reduce the work function.
- When light of suitable frequency is incident on the cathode, it emits the photoelectrons.
- These photoelectrons are attracted by the anode which is positively charged.
- This flow of electrons result in a flow of current.
- The flowing current is proportional to the intensity of incident radiation.
- This current may be further increased by filling some inert gas like argon into the glass.
- The photoelectrons emitted by cathode ionize the gas by collision.
- This collision results in increasing the current.
- The positive ions move towards the cathode.
- Negative ions and electrons move towards the anode.
Obviously, there is no conduction in the absence of light in the phototube.
Applications of Photoelectric Cell-
Photoelectric cell has its applications in the following-
- Burglar alarm
- Counting machines
- Street lights
- Home security system
- Fire alarm
1. Burglar Alarm-
- A burglar alarm is fitted near the lock of almirah.
- A thief comes and makes the light fall on the lock by match stick, torch etc.
- The light is received by the photoelectric cell.
- The flow of electrons start from cathode to anode.
- This completes the circuit and alarm starts ringing.
2. Counting Machines-
- Counting machines may be operated by using a photoelectric cell.
- Whenever a currency note obstructs the incident light, flow of current stops for that duration.
- This advances the machine by count one.
3. Street Lights-
- Street lights may be operated by using a photoelectric cell.
- The switch of the relay is attached with the photoelectric cell.
- When the intensity of sunlight decreases below the required value, the switch is activated.
- This switch on the street lights automatically.
4. Home Security System-
- In a home security system, the light is produced by a source at one end of the circuit.
- This light falls on a photoelectric cell sensor located at some distance away from it.
- The electrons are emitted by the cathode.
- When somebody walks between the light source and the sensor, the path of the beam is blocked.
- The sensor registers a drop in light levels and sends a signal to the control box.
- The control box is connected to either siren or a telephone autodialer.
- The control box on receiving the signal responds accordingly.
5. Fire Alarm-
- A photoelectric cell with a required circuit is installed in sensitive places.
- When the fire breaks out, light falls on the photoelectric cell.
- This causes the photoelectric emission which causes the current flow.
- This makes the bell connected to the circuit start to ring.
To gain better understanding about Photoelectric Cell,
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